The photo-generated electrons also have a weak ability to reduce nitrate and nitrite [Eqs. (8)– (12)]. Doudrick et al.  have demonstrated that electrons could be used for photocatalytic reduction of nitrate. Because no treatment was taken to deal with the dissolved oxygen during the reaction, the reduction of nitrate and nitrite might compete by the oxidation of nitrite by oxygen (E?(O2/H2O) = 1.23 V; E?(NO3−/NO2−) = 0.94 V).